Recently, it has been increasingly customary to place a small portable electronic device, such as a portable terminal and an electronic watch, in a charger, which is also called a station, for charging of the electronic device, data transfer therebetween, etc. On that occasion, if charging, data transfer, etc. are performed through electrical contacts, a problem would occur in point of watertightness because the electrical contacts are exposed to the outside. For that reason, charging, signal transfer, etc. are desirably performed in a non-contact manner through electromagnetic coupling between coils disposed respectively in the station and the portable electronic device.
In such an arrangement, when a high-frequency signal is applied to the coil on the station side, an external magnetic field is generated to produce an induced voltage in the coil on the side of the portable electronic device. By rectifying the induced voltage with a diode or the like, a secondary battery incorporated in the portable electronic device can be charged in a non-contact manner. Also, through electromagnetic coupling between both the coils, signals can be bidirectionally transferred in a non-contact manner from the station to the portable electronic device or from the portable electronic device to the station.
For the coil on the station side and the coil on the portable electronic device side, it is required not only to establish electromagnetic coupling between them, but also to increase the efficiency of charging and signal transfer. Meeting those requirements has been tried conventionally by ensuring such a positional relationship that when the portable electronic device is placed in the station, planes of windings of both the coils lie parallel to each other and the centers of the coils are aligned with each other.
To provide the above positional relationship just by placing the portable electronic device in the station is however difficult due to, e.g., the accuracy with which the coils are disposed in the station and the portable electronic device.
Further, if charging is carried out in spite of the portable electronic device being not placed in the station, a high-frequency signal would be uselessly applied to the coil on the station side, thus resulting in wasteful consumption of power.
It is therefore thought that a mechanism of detecting the positional relationship between both the coils is essential to perform charging and signal transfer. A mechanism of mechanically detecting the positional relationship between both the coils through contacts, for example, raises a problem in point of watertightness as mentioned above. Thus, in the case of transferring power or signals through electromagnetic coupling between coils disposed in opposing positions, there is a demand for detecting the positional relationship between both the coils in a non-contact manner.
Accordingly, a first object of the present invention is to provide an electronic device and a control method for the electronic device, with which when power or signals are transferred through electromagnetic coupling between coils disposed in opposing positions in two or more separate devices such as a portable electronic device and a station, a position offset between both the coils and the absence of a device to be charged can be detected in a non-contact manner, and charging and data transfer can be controlled depending on a detected result.
Meanwhile, when a secondary battery is charged up to a desired capacity in the above arrangement, charging the secondary battery beyond the desired capacity is wasteful consumption of power and is uneconomical. Furthermore, there is a risk that charging beyond the rated capacity may cause a liquid leakage or the like. In the case of putting a secondary battery on charge, therefore, charging is desirably controlled depending on the recharge rate of the secondary battery. To that end, it is conceivable to estimate the recharge rate of the secondary battery from a terminal voltage of the secondary battery in the charge mode.
However, even if the terminal voltage of the secondary battery has reached, for example, almost the battery voltage in its fully charged state, it is not always sure that the secondary battery is charged up to near the predetermined capacity. Also, the terminal voltage of the secondary battery in the charge mode cannot be regarded as indicating a true secondary voltage because it increases due to the internal resistance. For those reasons, a method of precisely estimating the battery recharge rate from the terminal voltage of the secondary battery in the charge mode is not expectable.
A second object of the present invention is therefore to provide an electronic device and a recharge-rate estimating method for a secondary battery, with which a recharge rate of the secondary battery under charging can be estimated with a simple construction.
Additionally, in the case of transferring power through electromagnetic coupling between coils, even if a portable electronic device can precisely estimate a recharge rate of its secondary battery, charging cannot be controlled unless the battery recharge rate is informed to a station, because the power is transferred with operation of the station. A mechanism of informing the battery recharge rate through electrical contacts raises a problem in point of watertightness as mentioned above.
A third object of the present invention is therefore to provide an electronic device and a charging control method, with which even when charging of a secondary battery is made from a charging device to a charged device in a noncontact manner through electromagnetic coupling between coils disposed in opposing positions in two or more separate devices, a recharge rate of the secondary battery, etc. is informed to the charging device in a non-contact manner so that the secondary battery can be charged up to a desired capacity.